Pumping device

ABSTRACT

Apparatus for pumping a pulp suspension and simultaneous abduction of gas from the suspension is disclosed. The apparatus comprises at least one pulp pump including a pump housing with an inlet, a first outlet for the suspension, and a second outlet for the gas. The gas outlet is connected to at least one external vacuum pump by a gas conduit including a substantially vertical portion having a maximum height, located on a level above the pulp pump, and a flushing water supply for the supply of flushing water to the gas conduit connected above the substantially vertical portion of the gas conduit.

FIELD OF THE INVENTION

The present invention relates to a device for pumping a pulp suspensionand simultaneously abducting gas from the suspension. More particularly,the present invention relates to a pulp pump, which is connected to avacuum pump for evacuating gas, such as air, from the pulp in the pump.

BACKGROUND OF THE INVENTION

In connection with pulp pumps, gas following along with the pulp causesproblems during pumping therein, especially in centrifugal pumps. Thegas in the pulp accumulates in the form of bubbles, which accumulate infront of the impeller and thereby deteriorates the capacity of the pump.This problem can be eliminated by evacuating the gas from the space infront of the impeller of the centrifugal pump to a sealing space behindthe impeller and further out of the housing of the pulp pump, forexample by means of vacuum pumps of the liquid ring type. These vacuumpumps are often separate pumps, the suction pipe of which is connectedto the sealing space in the housing of the pulp pump. Alternatively,they can be designed as a separate vacuum impeller in the form of aliquid ring impeller located on the shaft of the pulp pump, so thatcommon operation for both impellers is obtained. In the last mentionedcase, however, the capacity of the vacuum pump is restricted for spatialreasons.

A system with an external vacuum pump comprises a pulp pump, which by apipe is coupled to a vacuum pump for the evacuation of gas. Such a pulppump is disclosed, for example, in Swedish Patent No. 467,466. The pipeusually includes a stop valve and a vacuum control means. Normally,flushing water is supplied to the pulp pump. The flushing water has theobject of preventing clogging of the pipe to the vacuum pump and ofdiluting the pulp in the space behind the pulp impeller. The stop valveis controlled by a control valve for the pulp pump, so that the stopvalve is opened at a predetermined setting of the control valve of thepulp pump. The vacuum control means is set so that at normal processconditions stable conditions are achieved.

Such a system has the disadvantage that a definite vacuum must be set inspite of the fact that the process conditions can vary. This implies,that an optimum vacuum cannot be maintained in each situation. As aconsequence, the system in certain cases can permit pulp fibers tofollow along with the gas through the pipe to the vacuum pump, whichresults both in fiber losses and in possible damage to the vacuum pump.A vacuum pump is constructed to pump gas, and fiber transfer constitutesa weakness, which reduces the reliability of the entire pulp pumpingsystem. In other cases, the pulp pump can operate with much too great anamount of gas in the pump housing, which reduces the efficiency of thepump and causes so much gas to remain in the pulp that disturbancesarise in subsequent process steps.

SUMMARY OF THE INVENTION

In accordance with the present invention, these and other problems havenow been eliminated by the discovery of apparatus for pumping a pulpsuspension containing a gas and for removing the gas from the pulpsuspension, the apparatus comprising at least one pulp pump including apump housing having an inlet for the pulp suspension, a first outlet forthe pumped pulp suspension, and a second outlet for the gas, at leastone external vacuum pump, a gas conduit for connecting the second outletwith the at least one external vacuum pump, the gas conduit comprising asubstantially vertical portion having a maximum height located above thepulp pump, and flushing water supply means for supplying flushing waterto the gas conduit, the flushing water supply means connected above thesubstantially vertical portion of the gas conduit. In a preferredembodiment, the apparatus includes a plurality of the gas conduits, acorresponding plurality of the pulp pumps and a plurality of theexternal vacuum pumps connected to the plurality of pulp pumps by thecorresponding plurality of the gas conduits.

In accordance with one embodiment of the apparatus of the presentinvention, the apparatus includes a plurality of the pulp pumps, and acorresponding plurality of the gas conduits, and includes a commonconduit connected to each of the plurality of gas conduits, and aplurality of the external vacuum pumps connected to the common conduit.

In accordance with another embodiment of the apparatus of the presentinvention, the maximum height of the substantially vertical portion ofthe gas conduit comprises at least a height corresponding to theatmospheric pressure plus a height corresponding to the pressure in thepulp pump inlet.

In accordance with another embodiment of the apparatus of the presentinvention, the apparatus includes vacuum control means for limiting themaximum vacuum in the apparatus.

In accordance with another embodiment of the apparatus of the presentinvention, the apparatus includes a plurality of stop valves locatedbetween each of the plurality of external vacuum pumps and the commonconduit whereby each of the plurality of external vacuum pumps can beconnected or disconnected from the common conduit.

In accordance with the present invention, these objects have thus beenrealized by the pulp pump being connected to an external vacuum by meansof a pipe which is formed in a substantially vertical portion, thehighest point of which is located at a level above the pulp pump, andupwardly in the vertical portion of the pump a means for supplyingflushing water is connected.

The height of the substantially vertical portion of the pipe should beat least the height (measured as a water column), which corresponds tothe atmospheric pressure, normally about 10 m, plus the height, whichcorresponds to the pressure in the inlet of the pulp pump. The suppliedflushing water flows down through the pipe to the pulp pump. The pipe isonly partially filled with water, so that the gas is permitted to passupwardly, while the fibers follow along with the water back to the pulppump. The water level in the pipe depends on the pressure in the pulppump, the design of the pulp pump and the setting of the vacuum pump.The water level will vary automatically depending on the processconditions.

The present invention now provides for fiber losses to be avoided or beessentially reduced. An optimum vacuum can be obtained at differentprocess conditions without the use of special control means. The stopvalve for the vacuum pump as well as the vacuum control valve can beeliminated. The demand for flusing water can also be reduced by up to80% due to the fact that no fibers are transferred to the driving liquidof the vacuum pump in the liquid ring. Used driving liquid can therebybe recycled as new driving liquid.

If for installational or other reasons it is not possible or desirableto achieve sufficient height of the pipe (see above), it can benecessary to control the vacuum system. The maximum vacuum must then belimited so that fibers do not follow along to the vacuum pump. This canbe achieved by vacuum control in a suitable way which, for example, cangive a signal when a maximum vacuum is exceeded.

According to one embodiment of the present invention, a pulp pump of thecentrifugal pump type is coupled by means of a pipe to a vacuum pumplocated at a higher level. Alternatively, the vacuum pump can be placedon an optional level in relation to the pulp pump, if the pipe from thepulp pump first extends upwardly to the required level, and from thereto the vacuum pump.

According to another embodiment of the present invention, two or morepulp pumps are coupled together to two or more vacuum pumps. All pulppumps are placed at a lower level than the vacuum pumps. The vacuumpumps are connected to a common pipe of coarser (larger) dimensions.This coarser pipe is located above the pulp pump, and from it extends asmaller substantially vertical pipe down to each of the pulp pumps forde-airing according to the invention.

A means for supply of flushing water is connected to each of the smallerpipes. According to this embodiment, a stop valve can be placed betweeneach vacuum pump and the coarser pipe in order to permit theswitching-on and switching-off of the vacuum pumps after demand, bothduring operation and in connection with maintenance or repair withoutdisturbing the operation and function of the pulp pumps. Also, thevacuum pumps can be placed on optional levels in relation to the pulppumps, if the pipes from the pulp pumps first extend upwardly to therequired level and from there to the vacuum pumps through the commoncoarser pipe.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is described in greater detail in the followingdetailed description with reference to the Figures illustratingdifferent embodiments of the present invention, as follows:

FIG. 1 is a side, elevational view of one embodiment of the apparatus ofthe present invention; and

FIG. 2 is a side, elevational view of another rembodiment of theapparatus of the present invention.

DETAILED DESCRIPTION

FIG. 1 shows a pulp pump 1 in the form of a centrifugal pump, which islocated at a first level. The pulp pump comprises a housing 2 with inlet3 and outlet 4, respectively, for the pulp suspension and an outlet 5for gas. The pump is driven by a motor 6. The housing 2 of the pulp pumpis connected by means of a pipe 7 to a vacuum pump 8 in the form of aliquid ring pump with associated motor 9. The vacuum pump is located ata second level, which is higher than the first level. The pipe 7 has asubstantially vertical portion, and a means 10 for the supply offlushing water to the pipe is connected above the vertical portion ofthe pipe.

FIG. 2 shows an installation with several pulp pumps and vacuum pumps ofthe type shown in FIG. 1. The same reference numerals as in FIG. 1 havebeen used. The pulp pumps 1 are located at a first level, and the vacuumpumps (8) at higher levels. The vacuum pumps 8 are connected to a commoncoarser pipe 11, which extends above the pulp pumps 1. A smallersubstantially vertical pipe 7 extends from the coarser pipe 11 down toeach pulp pump 1 for de-airing. A means 10 for the supply of flushingwater is coupled to each pipe 7. Between each vacuum pump 8 and thecoarser pipe 11 a stop valve 12 is inserted. In this manner, a vacuumpump can be disconnected for service, repair, exchange or the likewithout requiring a pulp pump to be cut off. It is also possible toreduce the number of vacuum pumps, because every pulp pump does not needa vacuum pump of its own.

Upon starting the installation, one vacuum pump 8 can suitably be takeninto operation, while the other vacuum pumps are idling, i.e. theassociated stop valves 12 are closed. With an increasing amount of gasthe pressure increases, i.e. the capacity of the vacuum pump is notsufficient. When a predetermined pressure has been reached, additionallyone vacuum pump is coupled-in by opening the associated stop valve 12,and so forth.

Although the invention herein has been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent invention. It is therefore to be understood that numerousmodifications may be made to the illustrative embodiments and that otherarrangements may be devised without departing from the spirit and scopeof the present invention as defined by the appended claims.

1. Apparatus for pumping a pulp suspension containing a gas and forremoving said gas from said pulp suspension, said apparatus comprisingat least one pulp pump including a pump housing having an inlet for saidpulp suspension, a first outlet for said pumped pulp suspension, and asecond outlet for said gas, at least one external vacuum pump, a gasconduit for connecting said second outlet with said at least oneexternal vacuum pump, said gas conduit comprising a substantiallyvertical portion having a maximum height located above said pulp pump,and flushing water supply means for supplying flushing water to said gasconduit, said flushing water supply means connected above saidsubstantially vertical portion of said gas conduit.
 2. The apparatus ofclaim 1 including a plurality of said gas conduits, a correspondingplurality of said pulp pumps and a plurality of said external vacuumpumps connected to said plurality of pulp pumps by said correspondingplurality of said gas conduits.
 3. The apparatus of claim 1 including aplurality of said pulp pumps, and a corresponding plurality of said gasconduits, and including a common conduit connected to each of saidplurality of gas conduits, and a plurality of said external vacuum pumpsconnected to said common conduit.
 4. The apparatus of claim 3 whereinsaid common conduit is larger than said plurality of gas conduits. 5.The apparatus of claim 1 wherein said maximum height of saidsubstantially vertical portion of said gas conduit comprises at least aheight corresponding to the atmospheric pressure plus a heightcorresponding to the pressure in said pulp pump inlet.
 6. The apparatusof claim 1 including vacuum control means for limiting the maximumvacuum in said apparatus.
 7. The apparatus of claim 3 including aplurality of stop valves located between each of said plurality ofexternal vacuum pumps and said common conduit whereby each of saidplurality of external vacuum pumps can be connected or disconnected fromsaid common conduit.